Action games
If you don't play games that much, there is a big chance you have played an action game, e.g. a shooter, at some point. This category is full of games that won't let you get bored.
Soldat
Hitman: Blood Money
Counter-Strike Source 2D
No Gravity
Call of Duty
Star Wars Battlefront II
Fruit Cowboy
Crossfire Europe
WarRock
Vice City Multiplayer
Doom 3
Blur
Bubble Bug
Vicecity Ultimate
Garry's Mod - Prop Hunt
Tumble Bugs
Vega Strike
Prince of Persia : The Sands of Time
Alien Shooter 2
Sleeping Dogs
Wolfenstein - Enemy Territory
Mafia II
Team Fortress 2
Contra Game
AirRivals
Medal of Honor
Secret World Legends
Ben and Ed
Mad Medley Battle
Discover FDM
Add-on support
You can get add-ons that download files/video from arbitrary websites.